Solid oxide fuel cells are well known, but have been limited to power sources that are not temperature cycled repeatedly. To be useful for an automotive power plant, a fuel cell needs to become operational quite fast, preferably faster than 5 minutes, more preferably less than two minutes and even more preferably less than 30 seconds. Energy requirements to keep a high temperature solid oxide type fuel cell hot all the time in an auto are prohibitive. Hence, as fuel cell would need to be heated almost every time an auto was used, the cell would need to withstand perhaps as many as 10 to 20 thousand heating cycles. Auxiliary electrical power units for long haul trucks would have similar requirements. Similar requirements would be needed for portable electric generators based on SOFC's, electrical power generating SOFC units for the home, small businesses or apartment complexes and other distributed electrical generation SOFC units.
Flexible thin ceramics have been described for example in co-assigned U.S. Pat. No. 5,089,455, some compositions of which would be useful electrolytes for fuel cells. Recently, U.S. Pat. No. 5,273,837 has described the use of such compositions to form a thermal shock resistant fuel cell.
The foregoing discussion is intended to show use of zirconia as an electrolyte is known, and use of ((LaSrMnO3) and other expansion matched electrically conducting perovskite structures are known for use as air side electrodes, as well as use of zirconia/nickel composites for fuel side electrodes. In addition, metals, intermetallics and LaCrO3 have been used for interconnect structures.
Notwithstanding, there continues to be a need for improved solid oxide fuel cells, particularly fuel cells capable of withstanding very high heating and/or thermal cycles cycles with enhanced electrical power output. Thus, electrolyte sheets need to be mechanically strong, to be capable of withstanding very high heating and/or thermal cycles, while simultaneously offering good ionic conductivity.